The invention relates to magnetic transducers for narrow track recording and/or playback and it is particularly useful with respect to transducers made of hard, brittle magnetic materials.
Magnetic transducers having notched poles to reduce recording track width are well known in the art. The notches are generally filled with a suitable nonmagnetic material, such as glass to avoid chipping and granular pullouts of the magnetic material in the transducing gap area.
One example of prior art magnetic transducers having protective glass pockets at the transducing gap and a method of manufacturing such transducers is described in U.S. Pat. Nos. 3,813,693 and 3,845,550 to B. Gooch and E. Schiller, which patents are commonly assigned to Ampex Corporation and are hereby incorporated by reference in this patent application. In these prior art transducers glass bonding of the transducing gaps and filling the notches with glass to obtain the protective pockets is provided simultaneously during a single glass bonding operation. In these and other well known glass filled transducers the glass is generally selected from a group referred to as low temperature glasses having a melting temperature generally below 600.degree. C. These glasses have a disadvantage when utilized in transducers made of hard, brittle magnetic material, such as ferrite, of having a substantially higher wear rate relative to that of the magnetic material, resulting in differential wear of the transducer. Consequently, in the above indicated applications it is desirable to utilize so called high temperature glasses which have compatible mechanical properties, including wear rate with the magnetic material. However the melting temperature of high temperature glasses, which is generally around 900.degree. C., exceeds a critical temperature at which the permeability and other magnetic characteristics of the magnetic material are impaired. It is a well know undesirable phenomenon that when these glasses flow into ferrite material at a temperature above their melting point, diffusion of glass into the ferrite takes place. The latter phenomenon is irreversible and therefore transducer efficiency is thereby permanently reduced.
On the other hand, low temperature glasses are known to have a relatively high lead content and when heated to their melting temperature they may chemically react with the particular magnetic material thereby impairing its magnetic properties.
In addition to the above-indicated disadvantages of prior art it is well known that higher temperatures increases undesirable occurence of gas bubbles in the glass. Therefore it would be desirable to fill magnetic transducers with glass or similar nonmagnetic material at lower temperatures, that is at higher viscosity of the material to reduce the occurence of gas bubbles therein.